MathewC wrote:I don't normally leave the portafilter in the machine for very long anyway.

You may be compromising the taste of your shots a bit with room temperature coffee in a room temperature PF. I find that I get the best shots when I leave the PF locked in loosely, so it reaches group head temp. I remove it only to grind into it, replacing and fully locking it back in place immediately after tamping (and weighing, if I do that -which is rare these days).

I love your handiwork! I don't think an o-ring or nonconducting washer will do much to reduce heat transfer into the handle, though - the threads are still in full contact with the PF. The only way to really isolate the handle would be to make a "timesert" or "helicoil" style of threaded insert from a material with very low thermal conductivity, e.g. teflon or nylon (both of which are readily available and have thermal conductivities of ~ 0.25). Use both the insert and an isolating washer of the same material (or groove the face of the handle and add an o-ring) to prevent any direct PF-to-handle contact. Drill and tap the PF hole for the threaded OD of the insert, and tap the bore to take the handle. I've never seen a nonmetallic commercial timesert or helicoil, so you'll probably have to make one. But it'll save you at least one burn annually if you leave the PF in the group head so it's at brew temp.

Titanium alloys are very difficult to machine. One of the problems is that their heat conductivity is so low that heat conduction is so small that there can be dangerous fires during machining. The 6% Al 4% V alloy has thermal conductivity about a third that of stainless steel alloys, which is already very low. I have never attempted to make any thing from Ti stock. I suspect a portafilter handle from it would remain cool enough to handle.

Machining Ti requires cutting tools with different rake etc from common metals, and getting a good finish takes some practice. It'd probably make a great PF handle, but you'll go through some expensive metal stock learning to do Ti well. I think it's a cool idea worth the effort and cost, if you have the patience & desire.

Looks great! Too bad about the heat though.